#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;

int main(){

    long long A, B, T, N, mi=1e18, x;
    cin >> A >> B >> T;

    N = min(A, (T+B-1)/B);
    for (long long y=0; y<=N; y++){
        x = (T-B*y+A-1)/A;
        mi = min(mi, A*x+B*y);
    }

    cout << mi << endl;

    return 0;
}